How to install 'brew' packages manually.

Currently when I use my 'brew' to upgrade, I got some errors that I can't download the packages from github. 

The error messages are something like this:

==> Upgrading 1 outdated package, with result:
macvim 7.4-70
==> Upgrading macvim
==> Downloading https://github.com/b4winckler/macvim/archive/snapshot-70.tar.gz
####################################                                      50.0%
curl: (33) HTTP server doesn't seem to support byte ranges. Cannot resume.
==> Trying a full download
##                                                                         3.7%
curl: (56) SSL read: error:00000000:lib(0):func(0):reason(0), errno 54
Error: Download failed: https://github.com/b4winckler/macvim/archive/snapshot-70.tar.gz

I don't know why but it seems that 'curl' just can't download the packages from github.

So I want to install the package manually:

1) Download 'https://github.com/b4winckler/macvim/archive/snapshot-70.tar.gz' manually. So now I have '~/Download/macvim-snapshot-70.tar.gz'.

2) Verify it is the right one (this step is optional, but highly recommended):
 - Open '/usr/local/Library/Formula/macvim.rb' and we can see that the files's sha1 checksum should be '66432ae0fe81b2787b23343b6c99ef81f6b52c3e'
 - Use 'shasum' (a command line tool comes with the system) to check the downloaded file, it should output the same checksum.

3) Now open 'usr/local/Library/Homebrew/download_strategy.rb', add a line:
 (it should start at line 62)
  # Private method, can be overridden if needed.
  def _fetch
    ohai "download to #{@temporary_path}"
    curl @url, '-C', downloaded_size, '-o', @temporary_path
  end

4) Run 'brew upgrade' again. It will fail, but it will also print more information we need:
==> Upgrading 1 outdated package, with result:
macvim 7.4-70
==> Upgrading macvim
==> Downloading https://github.com/b4winckler/macvim/archive/snapshot-70.tar.gz
==> download to /Library/Caches/Homebrew/macvim-7.4-70.tar.gz.incomplete
##                                                                         3.6%
curl: (33) HTTP server doesn't seem to support byte ranges. Cannot resume.
==> Trying a full download
==> download to /Library/Caches/Homebrew/macvim-7.4-70.tar.gz.incomplete
####                                                                       6.2%
curl: (56) SSL read: error:00000000:lib(0):func(0):reason(0), errno 54
Error: Download failed: https://github.com/b4winckler/macvim/archive/snapshot-70.tar.gz

Note the red line, now we know the file name should be 'macvim-7.4-70.tar.gz.incomplete'. So we just copy the file here.

5) cp ~/Download/macvim-snapshot-70.tar.gz /Library/Caches/Homebrew/macvim-7.4-70.tar.gz.incomplete

6) edit 'usr/local/Library/Homebrew/download_strategy.rb' again, comment the line after when added:
  # Private method, can be overridden if needed.
  def _fetch
    ohai "download to #{@temporary_path}"
    # curl @url, '-C', downloaded_size, '-o', @temporary_path
  end

7) Run 'brew upgrade' again.  Succeed!
==> Upgrading 1 outdated package, with result:
macvim 7.4-70
==> Upgrading macvim
==> Downloading https://github.com/b4winckler/macvim/archive/snapshot-70.tar.gz
==> download to /Library/Caches/Homebrew/macvim-7.4-70.tar.gz.incomplete
==> ./configure --with-features=huge --enable-multibyte --with-macarchs=x86_64 --enable-perlinterp --enable-rub
==> make
==> Caveats
MacVim.app installed to:
  /usr/local/Cellar/macvim/7.4-70

To link the application to a normal Mac OS X location:
    brew linkapps
or:
    ln -s /usr/local/Cellar/macvim/7.4-70/MacVim.app /Applications
==> Summary
🍺  /usr/local/Cellar/macvim/7.4-70: 1796 files, 28M, built in 74 seconds